Global warming will accelerate sea-level rises due to thermal expansion of seawater and the melting of land-based ice sheets. If current GCMs projections of a 4cm per decade rise are reasonable, sea level may stand at least half a metre higher by the end of the next century. This will seriously threaten many low-lying islands and coastal zones, rendering some countries uninhabitable (Lewis, 1988). Other impacts include the increased risk of coastal flooding (Kana et al., 1984; Titus et al., 1987) and salination of fresh groundwater supplies, exacerbated by an increasing occurrence of droughts or storms. Rapid sea-level rise would damage the coastal ecology, threatening important fisheries.
Changes in ocean circulation are also projected to occur as a result of changing global climate. This will not only influence marine ecosystems (due to changes in upwelling zones), but will dramatically affect regional meteorological patterns (in response to the shifting heat balance). Palaeoclimatic studies (e.g. Boyle & Keigwin, 1987; Boyle, 1988) have revealed that rapid circulation changes, within only a few decades, have occurred in the past.